I'm gettng NDRs for only a handful of accounts when sending email. It does not matter which domain is being emailed. In other words, all outgoing (non-local) email gets the following NDR
Your message did not reach some or all of the intended recipients.
Subject: Account Lockout (Event ID: 539) Alert on SERVER
Sent: 5/5/2008 12:24 PM
The following recipient(s) could not be reached:
sales@XXXXXX.com on 5/5/2008 12:24 PM
There was a SMTP communication problem with the recipient's email server. Please contact your system administrator.
<XXXXXXXX.org #5.5.0 smtp;550 you are not allowed to send mail to <sales@XXXXXX.com>>
Other accounts have no problem emailing the exact same user account.